Top 10 nasty noises revealed

12th October 2012 - Heightened activity between the emotional and auditory parts of our brain explains why the sound of chalk on a blackboard or a knife scraped over a bottle is so unpleasant.

In a study published in the Journal of Neuroscience, researchers reveal the interaction between the region of the brain that processes sound, the auditory cortex, and the amygdala, which is active in the processing of negative emotions when we hear unpleasant sounds.

The paper's lead author Dr Sukhbinder Kumar, from Newcastle University said in a press release: "It appears there is something very primitive kicking in. It’s a possible distress signal from the amygdala to the auditory cortex."

A better understanding of the brain’s reaction to noise could help in our understanding of certain medical conditions.

Emotions in control

Researchers at the Wellcome Trust Centre for Neuroimaging at UCL (University College London) and Newcastle University used functional magnetic resonance imaging (fMRI) to examine how the brains of 13 volunteers responded to a range of sounds. Whilst inside the scanner they rated the sounds from the most unpleasant to the most pleasing. Researchers were then able to study the brain response to each type of sound.

The scientists found that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects. The emotional part of the brain, the amygdala, in effect takes charge and modulates the activity of the auditory part of the brain so that our perception of a highly unpleasant sound, such as a knife scraping on a bottle, is heightened compared to a soothing sound, such as bubbling water.

Analysis found that anything in the frequency range of around 2,000 to 5,000 Hz was rated unpleasant. Dr Kumar explains: "This is the frequency range where our ears are most sensitive. Although there’s still much debate as to why our ears are most sensitive in this range, it does include sounds of screams which we find intrinsically unpleasant."

Medical application

Scientifically, a better understanding of the brain’s reaction to noise could help us understand medical conditions where people have a decreased sound tolerance such as hyperacusis, misophonia (literally a 'hatred of sound') and autism when there is sensitivity to noise.

Professor Tim Griffiths from Newcastle University, who led the study, said in a press statement: "This work sheds new light on the interaction of the amygdala and the auditory cortex. This might be a new inroad into emotional disorders and disorders like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds."

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